Cap sensitive ammonium nitrate-fuel oil explosive and a method of manufacturing the same



3,111,437 SIVE 1963 'KUMAO HINO ETAL CAP SENSITIVE 11111101111111 NITRATE-FUEL OIL EXPLO AND A METHOD OF MANUFACTURING THE SAME Filed Sept. 6, 1960 F/GI I l 3 4 Surfactant 76 $odium dinaphthylmefhane disu/fanate SE A kfimEE Kn t.

l I 40 60 Cartridge dlamafre mm uum\E AT gg. S nc u INVENTORS KUNAO Hmq MuTsuo YOlOGAWA SHIGEFUM ASMM mam/1cm omA ;4 TTORNE Y S United States Patent Quit CAP SENSITHVE AMMONIUM NHRATE-FUEL 0H.

EXPLOSHVE AND A METHGD 0F MANUFAC- TUBING THE SAME Kumao Hino, Mutsuo Yokogawa, Shigefumi Asaita, and

Geniehi ()kada, Sanyocho, Asa-gun, Yamaguchi-ken,

Japan, assignors to Nipp'on Kayakn Kabnshiki Keisha,

Tokyo, Japan, a corporation of Japan Filed Sept. 6, 1960, Ser. No. 54,089 Claims priority, application Japan Jan. 9, 1960 Claims. (Cl. 149-21) This invention relates to improvements in or relating to the composition of ammonium nitrate-fuel oil explosives extensively used for rock blasting and to the production of the same.

As compared to the industrial explosives in general, the explosives ofthis kind are considerably poor in sensitivity and it is thus impossible to initiate them directly with standard blasting caps or detonating fuses. In order to bring about a steady detonation with these ammonium nitrate-fuel oil explosives, a cartridge of large diameter, e.g., 4 inches or more, must be used in a big bore hole blasting wherein a great amount of dynamite and the like is used as a booster or inserted between the main charges, or a particularly strong detonating fuse must be used for that.

In such a mixture free from an explosive sensitizer as the ammonium nitrate-fuel oil explosive, the ammonium nitrate as an oxidizing agent and the fuel as a reducing agent must be so intimately mixed with each other that they will be readily reacted.

Thus, the extent to which the fuel may be distributed between the particles of the ammonium nitrate is an impor-tant factor affecting the detonation reaction. Accordingly it is necessary to use extremely finely divided particles of the ammonium nitrate, to select a fuel capable of being tightly bonded thereto and to mix them in such a .way as capable of combining them satisfactorily. Since it is difficult in principle to flully disperse the fuel oil in the ammonium nitrate which is hydrophilic in itself, it is obvious that there should be a limit to the combination thereof with a mere mechanical mixing.

It is an object of this invention to provide an ammonium nitrate fuel oil explosive which can be safely handled and readily made at low cost. It is another object of the invention to provide an ammonium nitrate-fuel oil explosive which can be initiated solely with a standard blasting cap without the use of a special booster and the like even in the small bore hole blasting. It is still another object of the invention to provide an ammonium nitrate-fuel oil explosive which is excellent in detonation ability. It is a further object of the invention to provide an ammonium nitrate-fuel oil explosive wherein a gas resulting from the explosion is a complete combustion gas.

In the drawings, "FIG. 1 is a graph showing the relation between the amount of a surfactant added and the det onation ability, and FIG. 2 is a graph showing the relation between the cartridge diameter and the detonation velocity.

According to the invention, there is provided an explosive consisting of ammonium nitrate, a liquid fuel oil having good fluidity and a particular surfactant or surface active agent. It has been found that a mixture which has an excellent sensitivity to the initiation thereof can be obtained by mixing the ammonium nitrate which is hydrophilic with the fuel oil which is lipophilic with the aid of the surfactant which combines the two main com ponents on a molecular scale.

The ammonium nitrate which can be used in this invention may be any of fertilizer grade or commercial grade. However, the particle size of the ammonium nitrate material should preferably be as small as possible since the particle size has a great effect upon the initiation sensitivity and the material should thus be crushed by an edge runner (pan mixer) or a hammer pulverizer (so-called micro atomizer) or the like. The fuel oil used may be of coal series such as coal tar and anthracene oil, or of petroleum series such as light oil. The coal tar herein referred to includes a crude coal tar produced by dry distillation of coal, and a refined coal tar. The refined coal tar is a mixture of a creosote oil produced as a fraction by dehydration and fractional distillation of the crude coal tar with a pitch as a distillation residue. It is a viscous liquid at the normal temperature which may be generally used for painting. As fuel oil, refined coal tar can be used as well as crude coal tar. The anthracene oil used is a fraction of the coal tar at about 300 C. having the ignition point of about 200 C. and the viscosity similar to the heavy oil. The light oilused may be one used as a diesel oil with the ignition point of C. The viscosity thereof is small.

The mixing proportions of these fuel oils to the ammonium nitrate are 4 to 7% on the whole in the oxygen balanced mixture though they depend upon the particular fuel oil used or the amount of an anionic surfactant used as hereinafter described. However, when the oxygen balance does not cause a great problem as is the case with the open pit, the practical range thereof may be 2 to 10% of the whole mixture.

A surfactant which acts as the effective third component of the above ammonium nitrate-fuel oil mixture and remarkably promotes the initiation sensitivity thereof is an anionic surfactant having a very strong hydrophilic activity, the examples of which being sodium dinaphthylmethane disulfonate, or sodium alkylsulfate or sodium alkylbenzene sulfonate having an alkyl group of 10 to 14 carbon atoms.

These anionic surfactants are all free of odor and in a powdered form, so that they can be easily handled. With a commercial product, there may be some sodium sulfate or other builders entrained without It is believed that when the anionic surfactant is incorporated into the ammonium nitrate-fuel oil mixture having the proportion as set forth hereinbefore, it is coordinated between the two components wherein its hydrophilic groups are directed to the ammonium nitrate and combined with N0 groups thereof on a molecular scale while the lipophilic groups tightly combined with the fuel oil, whereby contact between the first two components is developed to a greater extent than in the absence of an anionic surfactant, and a molecular combination is established between the oxidizing agent (ammonium nitrate) and the reducing agent (fuel oil) with the anionic surfactant as a bridge.

When the ammonium nitrate-fuel oil mixture which is substantially in a molecular combination with an anionic surfactant as a bridge is initiated by means of a blasting cap, it will act as a initiation center and transmit detonation rapidly and accurately wherein the initiation sensitivity and the detonation ability of the mixture are promoted as a whole.

Since the above anionic surfactant will act on the boundary surface of the ammonium nitrate-fuel oil mixture, the required amount for use is small, that is, about 0.1% of the entire composition will suffice for effective operation and the use of about 0.5 to 1.0% will bring about an approximate equilibrium with respect to the effect of the composition.

This may be demonstrated by FIG. 1 in which an explosive was prepared in a manner similar to that of Example 1 hereinafter described using sodium dinaphthyl methane disulfonate or sodium lauryl sulfate as an anionic surfactant. in the graph of l, the proportion percent of sodium dinaphthylemethane disulfonate or sodium lauryl sulfate to the whole mass was taken as the abscissa and the value of the critical diameter (hereinafter defined) as the ordinate which value reflects the detonation ability of the explosive prepared by the use of the above material.

In any case it will be seen that the value of the critical diameter is subjected to a considerable change with the addition of 0.1% of the anionic surfactant and kept substantially constant with the addition of 0.5 to 1.0% thereof. It is, of course, understood that on an economical basis the amount of anionic surfactant to be added should preferably be as small as possible, but the practical range may be up to to prevent any possible insufficient mixing.

As set forth above, it is a pre-requisite to increase the extent of physical bondage between each component in order to facilitate formation of molecular combination between the ammonium nitrate and the fuel oil.

To accomplish this object, it is most efiective to adopt a method of milling and mixing by the use of an edge runner and it is also desirable to change the materials in the order of ammonium nitrate, anionic surfactant and fuel oil. Alternatively, the ammonium nitrate which has been finely divided in a hammer pulverizer and the like may be mixed with other components in a simple mixer commonly used. The resulting ammonium nitratefuel oil explosive exhibits an excellent initiation and detonation ability particularly when the particle size of the ammonium nitrate thereof is such that more than 40% of the material may pass through a 200 mesh Tyler standard sieve.

As a factor for increasing the extent of physical and chemical combination of each component, the temperature at the time of mixing should naturally be taken into consideration. In milling and mixing by means of an edge runner when the coal tar is used as a fuel oil, the temperatures of the edge runner beteen 85 and 95 C. are most effective in the promotion of the detonation ability of the product. On the other hand, anthracene oil or light oil have good miscibility with ammonium nitrate at room temperature and the mixing process may be effected at room temperature. Practically speaking, the mixing of each component may be effected at the normal temperature irrespective of whether the edge runner is used as a mixer or the commonly used simple mixer is used with the finely divided ammonium nitrate, so long as the atmospheric condition is used under which the ammonium nitrate is not hygroscopic. Under the atmospheric condition of high humidity under which the ammonium nitrate tends to be hygroscopic, the mixing may be effected at a temperature to C. higher than the atmospheric temperature or under condition shut oif from the atmosphere. At a low atmospheric temperature the coal tar becomes viscous, which makes it dilfcult to be dispersed Well between particles of the ammonium nitrate. In such a case, the coal tar may be subjected to mixing while heated at 20 to 40 C.

As mentioned above, the product of this invention obatined by the above mixing method with the use of the indicated anionic surfactant will be completely detonated with a cartridge diameter of 20 to mm. and by the sole use of No. 6 blasting cap. The detonation ability thereof is also excellent and the Whole power is much the same as that of the conventional industrial explosive.

In the ammonium nitrate-fuel explosives, the emission of red fume after blasting is so severe that the use thereof underground is practically impossible. Contrary to this, the detonation ability of the product of the invention is so excellent that the gas emitting after blasting can be tolerable as in the case of the general industrial explosive. Thus the product of the invention is prac- 4g, tically suitable as an explosive for underground use which may be evidenced by the Table 1 below.

TABLE 1 Amount of gas generated from 1 kg. of sample Explosives C O l. Nitrose, 1.

Sample 1 38. (i 2.26 Semi gelatin 4 2. 20

NOTE: Sample 1 may be obtained according to the method of Example 1 hereinafter described. The composition of semi-gelatin is 10.5% nitroglycerine gel, 5.0% nitro compound, 76.0% ammonium nitrate and 8.5% wood meal.

The product of the invention can be stored for a long time. As a result of storage of more than six months, it did not harden at all, its detonation ability being kept constant.

The embodiment of the invention will be illustrated by the following specific examples, which are merely illustrative and not to be construed for limitation.

in the examples, it is understood that the test of the initiation ability of such a very dull explosive as the ammonium nitrate-fuel oil explosive comes first. For this purpose we inventors devised a practical minimum diameter test, which was used in the examples. Thus, a mixture was charged in a paper shell of a particular diameter (the length of charge was 230 mm. irrespective of the diameter), which was placed on a sand bed and initiated by means of No. 6 blasting cap. In this case, the extent of detonation of the mixture may be determined by observing the crater produced in sand and the residue of the cartridge after detonation. The presence of a bit of cartridge residue, large and small, means incomplete or failure detonation. At least 10 shots are fired for the same cartridge. The minimum diameter at which 100% complete detonation takes place is defined as the practical minimum diameter, the diameter at which 50% complete detonation takes place as the critical diameter and the diameter at which 0% detonation takes place as the failure diameter. The smaller these values are, the better is the initiation sensitivity of the cartridge.

Example 1 93.3% of ammonium nitrate was charged into an edge runner and crushed and dried with heat. Then 0.7% of sodium dinaphthylrnethane disulfate Was added while heating was continued up to the charge temperature of to C. When this temperature was reached, the heating operation was stopped but the crushing and agitating operation continued. Thereafter 6.0% of crude coal tar was added thereto with sufficient mixing and the resulting mixture was withdrawn from the edge runner and allowed to stand for cooling to the normal temperature. By screening the mixture using a 12 mesh Tyler standard sieve, the agglomerated mass was loosened and the foreign material was removed. Then the product was packed for final use. The mixture of the product was referred to as sample 1. Another product prepared in a similar manner from the material consisting of 93.5% of ammonium nitrate and 6.5% of crude coal tar (referred to as sample 0) was compared with the above product of the invention. The result was as follows.

Practical Detonation velocity minimum (m., sec.)

diameter Sample 0 t. 50 3, 600 3, 400 Sample 1 22 4,140 4,400

packed (sample 4).

Example 2 A mixture of 93.3% ammonium nitrate, 6.0% of crude coal tar and 0.7% of sodium lauryl sulfate,

C H OSO Na was prepared under the same conditions as that of Example 1. The mixture (sample 2) was compared with the sample 0. The result was as follows:

Practical Detonation minimum velocity diameter A (rm/sec.)

Sample 50 3, 600 Sample 2 22 4, 210

Example 3 A mixture of 93.3% of ammonium nitrate, 6.0% of crude coal tar and 0.7% of sodium dodecylbenzene sulfonate,

C 12H25-S OaNtl was prepared under the same conditions as that of Example 1. The mixture (sample 3) was compared with the sample 0. The result Was as follows.

Practical Detonation minimum velocity diameter A (m./sec.)

Sample 0 50 3, 600 Sample 3 24 4, 000

Example 4 93.3% of ammonium nitrate was charged into an edge runner and crushed while it was heated to 40 C. at which temperature the ammonium nitrate was not hygroscopic irrespective of the atmospheric conditions (atmospheric temperature: 30 C., humidity: 90%). Then 0.7% of sodium lauryl sulfate was added thereto with sufiicient mixing, after which 6.0% of anthracene oil was added and mixed until a homogeneous composition was obtained. Then the mixture was withdrawn from the edge runner and allowed to stand for cooling to the normal temperature. Thereafter it was screened by means of a 12 mesh Tyler standard sieve to loosen an agglomerated mass and remove foreign materials, and The property of this explosive was as follows.

Practical Detonation minimum velocity diameter A (m./see.)

Sample 4 24 4. 050

Example 5 cient mixing while the material was conveyed by a screw conveyor to a hopper. The resulting mixture was with drawn from the hopper to a vessel for packing (sample 5). The property of the sample was as follows.

Detonaton velocity A (m./sec.)

Sample 5 25 4, 00

Example 6 Practical minimum diameter (mm.) Sample 6 25 Sample 6 45 Example 7 92.6% of ammonium nitrate was crushed according to the method of Example 5, which was added and mixed with 3.0% of sodium lauryl sulfate and 4.4% :of anthracene oil in a manner similar to that of Example 5 to produce a sample 7. Comparison of the sample with the sample 6' was shown below.

Practical minimum diameter (mm.) Sample 7 25 Sample 6 45 Example 8 93.2% of ammonium nitrate was crushed according to the method of Example 5 and added and mixed with 1.0% of sodium dinaphthylmethane disulfonate and 5.8% of crude coal tar in a manner similar to that of Example 5 to produce a sample 8. In this case, the crude coal tar was comparatively viscous and thus the mixture was maintained at above 25 C. to facilitate mixing. The property of the sample was as follows.

Practical minimum diameter (mm.) Sample 8 25 Example9 94.4% of ammonium nitrate was crushed according to the method of Example 5 and then added and mixed with 1.0% of sodium dodecylbenzene sulfonate and 4.6% of light oil in a manner similar to that of Example 5 to produce a sample 9. The result of test of the sample was as follows.

Practical minimum diameter (mm.) Sample 9 25 What We claim is:

1. A cap sensitive ammonium nitrate-fuel oil explosive consisting of 2 to 10% by Weight of a fuel oil selected from the group consisting of coal tar, anthracene oil and light oil, 0.1 to 5% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms, and ammonium nitrate, more than 40% of said nitrate being .finely divided particles which pass through a 200 mesh Tyler standard sieve.

2. A cap sensitive ammonium nitrate-fuel oil explosive as claimed in claim 1 wherein the anionic surfactant is 0.1 to 1.0% by weight and the fuel oil is coal tar in the amount of 5.5 to 7.5% by weight.

3. A cap sensitive ammonium nitrate-fuel oil explosive as claimed in claim 1 wherein the anionic surfactant is Z 0.1 to 1.0% by weight and the fuel oil is light oil in the amount of 4.0 to 6.0% by weight.

4. A cap sensitive ammonium nitrate-fuel oil explosive as claimed in claim 1 wherein the anionic surfactant is 0.1 to 1.0% by Weight and the fuel oil is anthracene oil in the amount of 5. to 7.0% by weight.

5. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve while heating the same, concurrently adding thereto 0.1 to by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has to 14 carbon atoms, discontinuing the heating when the temperature of the ammonium nitrate reaches 85 to 95 C., adding 2 to 10% by weight of coal tar, and cooling the mixture to ambient temperature while crushing and mixing are further continued.

6. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve while heating the same to a temperature 10 to C. higher than ambient temperature, adding thereto 0.1 to 5% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate Whose alkyl group has 10 to 14 carbon atoms, adding thereto 2 to 10% by weight of anthracene oil, and continuing the crushing and mixing.

7. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve while heating the same to a temperature 10 to 20 C. higher than ambient temperature, adding thereto 0.1 to 5% by Weight of an anionic surfactant selected fro-m the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms, adding [thereto 2 to 10% by Weight of light oil, and continuing the crushing and mixing.

8. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises mixing at a temperature of 20 to 40 C. ammonium nitrate containing more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve, with 2 to 10% by Weight of coal tar and 0.1 to 5% by Weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms.

9. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises mixing at a temperature 10 to 20 C. higher than atmospheric temperature ammonium nitrate containing more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve, with 2 to 10% by weight of anthracene oil and 0.1 to 5.0% by Weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms.

10. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises mixing at a temperature 10 to 20 C. higher than atmospheric temperature ammonium nitrate containing more than 40% of finely divided particles passing through a 8 200 mesh Tyler standard sieve, with 2 to 10% by Weight of light oil and 0.1 to 5.0% by Weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulf-ate, and sodium alkylbenzene sulfonate Whose alkyl group has 10 to 14 carbon atoms.

11. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve while heating the same to 20 to 40 0., adding thereto 0.1 to 5.0% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylrnethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene ulfonate whose alkyl group has 10 to 14 carbon atoms, adding thereto 2 to 10% by weight of coal tar and continuing the crushing and mixing.

12. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate at normal temperature until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve, adding thereto 0.1 to 5.0% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms, adding thereto 2 to 10% by weight of anthracene oil, and continuing the crushing and mixing.

13. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises crushing ammonium nitrate at normal temperature until it contains more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve, adding thereto 0.1 to 5.0% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane disulfonate, sodium alkylsulfate, and sodium alkylbenzene sulfonate Whose alkyl group has 10 to 14 carbon atoms, adding thereto 2 to 10% by weight of light oil, and continuing the crushing and mixing.

14. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive Which comprises mixing at atmospheric temperature ammonium nitrate containing more than 40% of finely divided particles passing through a 200 mesh Tyler standard sieve, with 2 to 10% by weight of anthracene oil and 0.1 to 5.0% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane, sodium alkylsul fate, and sodium lalkylbenzene sulfonate Whose alkyl group has 10 to 14 carbon atoms.

15. A method for the manufacture of a cap sensitive ammonium nitrate-fuel oil explosive which comprises mixing at atmospheric temperature ammonium nitrate containing more than 40% of finely divided paltticles passing through a 200 mesh Tyler standard sieve, with 2 to 10% by Weight of light oil and 0.1 to 5.0% by weight of an anionic surfactant selected from the group consisting of sodium dinaphthylmethane, sodium. alkylsulfate, and sodium alkylbenzene sulfonate whose alkyl group has 10 to 14 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,975,046 Cooley et al. Mar. 14, 1961 FOREIGN PATENTS 219,886 Australia Feb. 2, 1959 152,199 Great Britain Oct. 14, 1920 146,308 Sweden July 27, 1954 

1. A CAP SENSITIVE AMMONIUM NITRATE-FUEL OIL EXPLOSIVE CONSISTING OF 2 TO 10% BY WEIGHT OF A FUEL OIL SELECTED FROM THE GROUP CONSISTING OF COAL TAR, ANTHRACENE OIL AND LIGHT OIL, 0.1 TO 5% BY WEIGHT OF AN ANIONIC SURFACTANT SELECTED FROM THE GROUP CONSISTING OF SODOIUM DINAPHTHYLMETHANE DISULFONATE, SODIUM ALKYLSULFATE, AND SODOIUM ALKYLBENZZENE SULFONATE WHOSE ALKYL GROUP HAS 10 TO 14 CARBON ATOMS, AND AMMONIUM NITRATE, MORE THAN 40% OF SAID NITRATE BEING FINELY DIVIDED PARTICLES WHICH PASS THROUGH A 200 MESH TYLER STANDARD SIEVE. 